I haven't really gotten the hang of it... I've just been gathering people into circles like it's some sort of collection.
I can't figure out when I would want to use it, but the same could have been said for twitter when I first joined that, and now I'm completely addicted (@Baconeer if you wanna follow me).
But if anyone wants to add me on Google+, I'm "Amanda Strassner", the only one with that name last I checked.
I can also invite people if you want in! But Google keeps closing it down so that even if you're invited you might not be able to join yet. Not sure what the current status is.